The club-shaped tenderloin is located under the long loin and abuts the spine.
The narrow end of the tenderloin is the filet part of a T-bone steak; towards the butt as the filet increases in size and diameter it becomes part of a Porterhouse steak.

Depending on the overall size of the bison, the tenderloin is usually about 18 inches long.
At the narrow end it can measure as little as an inch in diameter.
At the butt end it can be as much as 4 inches in diameter

The narrow end, the last 4 inches or so, can be grilled whole, or sliced up for a stir fry.
The abutting small centre section is the filet mignon, which can be cut into steaks and grilled, or be used in recipes calling for medallions, or tournedos.
The centre section, closest to the butt end, can be cut into 2 to 3 inch sections for Chateaubriand steaks

The tenderloin is actually two muscles.
The bulk of the tenderloin is the main muscle, but alongside most of it runs a thin muscle known as the 'bavette' or chain muscle.
It is easily separated from the main muscle and can be grilled or sliced up for a stir fry.
But what I have done here is tie it snugly against the main tenderloin muscle so it won't separate while being roasted.

The tenderloin roast used in this recipe was a little over 2 lbs.-enough to serve 4 or 5 people.
It included the butt end, the Chateaubriand section, and a very small part of filet mignon section.
That way, with thickness not varying all that much from the butt end to the filet mignon, even roasting and doneness was assured

I find the best way to roast tenderloin is by pan searing first, then finishing it in a low heat oven.

First, from the refrigerator, allow the tenderloin to stand at room temperature for one hour.
Set your oven at 225F.
Pat the tenderloin dry with kitchen towel before tying it off with butcher cord in 1 ½ to 2 inch intervals.

Over moderately high heat, bring 1 ½ tbsp unsalted butter or ghee to the point of near smoking in a large heavy saucepan.
Sear the roast until browning is noticeable.
In total, searing should take about 6 to 8 minutes.

Transfer the roast to a wire rack set over a roasting pan.
Lightly salt and pepper the roast.
Insert the probe of a digital meat thermometer into the centre of the roast.

For rare, roast until the thermometer reads 115F (usually 45 to 50 minutes), then turn off the oven leaving the oven door closed.
Allow the roast to reach 125F (about 12 to 15 minutes longer), before removing roast from the oven.

For medium-rare (shown in photograph), roast until thermometer reads 125F (usually 55 to 60 minutes), then turn off the oven leaving the oven door closed.
Allow the roast to reach 135F (about 12 to 15 minutes longer), before removing roast from the oven.

Allow the roast to rest on the carving board for 15 minutes before slicing.
Serve on warm plates with desired accompaniments and get ready to enjoy the best meat treat of your life!